Cracking: Breaking up larger molecules

Cracking in petro chemistry, organic chemistry and petroleum geology is the process in which complex large hydrocarbons are broken down into lighter hydrocarbons molecules, by breaking carbon-carbon bonds. The end products from this process are strongly dependent on the temperature and catalysts present. For the commercial production of gasoline and diesel, Cracking is the most important process.

Chemistry in Cracking:

During the cracking process, huge number of chemical reactions takes place. Most of the reactions which take place are free radicals based. Following are the main reactions that take place during cracking:

Initiation:

A single molecule of an element breaks down into two free radicals in these initiation reactions. Only few portions of the feed molecules undergo these reactions but initiation is important for producing the free radicals which drives the rest of the reactions.

Hydrogen abstraction:

In hydrogen abstraction a hydrogen atom is removed from another molecule by a free radical, which turns second molecule as a free radical.

CH3• + CH3CH3 → CH4 + CH3CH2•

Radical decomposition:

During these reactions a free radical breaks into two molecules; alkene and a free radical. This is the process whose outcome is alkene products.

CH3CH2• → CH2=CH2 + H•

Radical addition:

It is the reveres of radical decomposition reaction; a radical reacts with an alkene forming a large single radical. These reaction forms aromatic products.